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Covered conductors - A solution for outage reduction in thick vegetation areas.

Vegetation growth is a major cause of frequent and prolonged outages to ECG’s rural and some peri-urban areas. The outgrown tree branches along the paths of the ECG network poses a great challenge to ensuring constant supply of power to our customers within these operational areas. These vegetation causes frequent outages (Light off) in the system due to momentary phase to phase clashes during windy conditions or sustained bridging of all phases when a tree branch falls on the lines. This explains the outages customers experience

when it rains or during windy conditions. Due to the long nature of some of our lines (feeders), our engineers will have to patrol the whole line to find out the location of the tree branch causing the outage to restore power to customers. However, if our engineers are lucky and it is transient (unsustained) fault, a simple reset of the control switch (trial switching) can restore power back to customers.

 Bamboo branches on the 33kV line at Tarkwa Nsuaem

ECG uses primarily bare aluminium conductor for the construction of our lines. The use of bare conductors (All Aluminium Alloy Conductors) though very economical results in a lot of outages especially in forested areas simply because of the reasons raised above. Vegetation control have not adequately addressed the issues with outages in forested areas due to the fact that the trees in these areas have a growth rate faster than frequency of bush clearing activities especially in predominantly Bamboo prone areas.

In a bid to minimize the effect of over grown vegetation along the paths of our lines in the provision of reliable source electricity supply to our cherished customers, ECG has already adopted the use of 11kilovolts covered conductors within the 11kilovolts and its low voltage network to reduce outages due to vegetation problems. The effect of this has been evaluated over the years and has been found to be very successful.

Management in a bid to transfer the success story to the 33kilovolts network, approved a proposal to pilot the use of 33kV covered conductors and its associated accessories to address the same problem with the 33kV distribution network. This type of covered conductors has been extensively used in Scandinavian countries for the past 40years.

A section  of the 33kV conductor constriction at Tarkwa Nsuaem

A 10km portion of the Agona feeder was selected in consultation with our Western Regional operations team for the pilot. The portion of the feeder to be reconductered runs through thick Plantation Forest from Apimanim Junction to Nsuaem. The trees along the path of this line cannot be felled either on the basis of exorbitant cost of compensation to be paid to the owners or breach of environmental laws of our State. Thereby limiting us to branch trimmings which does not really eradicate the effect of these tress on our lines.

4 spans of the covered conductor construction

 The objectives of the pilot project included the following:

  1. Reduce downtime of the feeders
  2. Improve upon ECG’s reliability
  3. Increase ECG revenue through availability and usage
  4. Increase customer satisfaction
  5. Ease of maintenance and operation activities

The project execution was strictly managed by a team comprising of our regional project team which provided day-to-day supervision to ensure that the contractor worked in accordance with the specifications and construction standards of ECG and the technical requirements of the cable manufacturers and a team from the Special projects Division that visited site bi-weekly to address all challenges and remove all bottlenecks to ensure that the project progressed according to scope, cost, time and quality.

The project team upon the start of the project gathered the outage statistics of the chosen line and did same upon completion. The team then undertook a financial and economic analysis of the outage statistic gathered over a period of three months after project completion and compared the results to the existing situation. The results of the analysis coupled with feedback from other stakeholders such as our cherished customers within the catchment area of this line and the western regional line maintenance team, indicates an achievement of the set objectives of the project.

Though the project has a negative Financial Net Present Value(NPV), the economic NPV is positive. The negative Financial NPV is typical of every reliability project since the main focus is to improve the quality of supply rather than a financial gain therefore the economic analysis outweighs that of the financial.

It is recommended that the use of 33kV covered conductors be adapted fully by ECG to solve issues with overgrown vegetation inferring from the fact that installation of 33kV covered conductors have brought a huge relief to residents of Tarkwa Nsuaem and its environs as well as the ECG maintenance team.

 

By Ing. Frederick Kwabena Bediako

Manager/Major Projects (Ashanti SBU)

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